Touchless TFT panel lamination fixture and process

ABSTRACT

A method and apparatus for laminating a TFT panel with a glass support plate without the need to touch an active area of the TFT panel. To accomplish this result, a touchless vacuum lamination chuck secures the TFT panel by its outer margins that do not carry TFTs. To facilitate lamination of the TFT panel, a pressure chamber is formed within the laminating chuck to provide support to the center region of the TFT panel as it is brought into contact with the glass support plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of commonly owned, co-pendingprovisional application Ser. No. 60/525,481, filed Nov. 25, 2003 andentitled “TOUCHLESS TFT PANEL LAMINATION FIXTURE AND PROCESS”, theentire contents of which are incorporated by reference herein.

FIELD

This patent specification relates to laminating a TFT panel with a glasssupport plate. More particularly, this patent specification pertains toa method and apparatus for laminating a TFT panel with a glass supportplate while refraining from making contact with any portion of the TFTpanel's front face other than on peripheral strips that are free ofTFTs.

BACKGROUND

Thin film transistor (TFT) panels are frequently fabricated on very thinsubstrates such as 0.7 mm thick glass panels. The back faces of the TFTpanels, i.e. the sides opposite the front faces carrying the TFTs, aresubsequently laminated onto glass support plates, commonly using aUV-curable resin, so that subsequent process steps can be performedwithout damaging or distorting the fragile TFT panels. This approach iswell known in the art and is described in U.S. Pat. No. 5,827,757 issuedOct. 27, 1998 to Robinson, et al., which is hereby incorporated byreference. During this process, solid objects should not make contactwith the front face of the TFT panel because burrs or dust particlesfound on solid objects can crush films on the TFT panel.

A previous approach for laminating a TFT panel onto a glass supportplate involves holding the TFT panel using a vacuum chuck with a pieceof lint-free paper forming a cushion between the chuck and the frontface of the TFT panel to avoid having the metal chuck make directcontact with the front face of the TFT panel. Lint-free paper can beused as a cushion because it is both porous and cushioning. Panellaminated according to this approach are offered commercially in thiscountry by the assignee hereof, and further information therein isavailable at its website, HOLOGIC.COM.

Artifacts can sometimes be found on images captured using TFT panelsthat have been manufactured using lint-free paper. These artifacts are aresult of uneven curing of UV resin used in the TFT panels due toreflection of UV light from the lint-free free paper to the TFT panels.Lint-free paper can also leave small paper particle on the TFT panelthat must subsequently be removed using a spin cleaning process. Spincleaning can add cost and complexity to the TFT panel manufacturingprocess and can occasionally promote crazing of the TFT panel therebylowering the manufacturing yield. The vacuum chuck used in this processdoes not shield the TFT panel from potentially harmful vapors thatemanate from the UV-curable resin used to laminate the TFT panel to theglass support plate.

SUMMARY

An object of the disclosed system and method is to solve problemsdiscussed above relating to laminating TFT panels onto glass supportplates.

Specifically, an object is to provide a system and method for laminatingTFT panels onto glass support plates without making contact with thefront face of the TFT panel (the face carrying the TFTs) other than onperipheral strips that are free of TFTs. It is also an object to providea system and method for laminating TFT arrays onto sturdy glass plateswithout the use of lint-free paper. It is also an object to reduceartifacts found on images captured using TFT panels relative to imagescaptured from TFT panels manufactured using a previous approachinvolving lint-free paper. It is also an object to provide a system andmethod for laminating TFT panels onto glass support plates that mayavoid the need for spin cleaning, shield the TFT panel from potentiallyharmful vapors that emanate from UV-curable resins used to laminate theTFT panel to the glass support plate, and reduce instances of crazingover TFT panels that have been laminated pursuant to the previousapproach.

The disclosed system and method laminate TFT panels onto glass supportplates without making contact with the front face of the TFT panel otherthan on peripheral strips that are free of TFTs, while reducingartifacts found on images captured using TFT panels, avoiding the needfor spin cleaning, shielding the TFT panel from potentially harmfulvapors that emanate from UV-curable resins, and reducing instances ofcrazing.

The disclosed system comprises a lamination chuck which contacts the TFTpanel only on the peripheral strips. The TFT panel is orientedhorizontally with the face to be laminated (the back face) facing up andthe sensitive front face facing down. The TFT panel is supported by acushion of gas, preferably dry nitrogen (N₂), to prevent the thin TFTpanel from sagging under its own weight and to cause the TFT panel tobow up at the start of the lamination process. The gas is prevented fromescaping by sealing the perimeter of the lamination chuck with sealingtape. The pressure within the cushion of gas is monitored by a manometerand regulated by a bleed valve, a gas inlet, and a pressure regulator.The peripheral strips are held to the chuck by vacuum channels that arebuilt into the rim of the chuck. While the TFT panel is held firmly inplace and bowed up, a UV-curable resin is applied to the TFT panel. Theglass support plate is gradually brought into contact with the TFT panelas the pressure within the cushion of gas is reduced. The resin spreadsout as the area of contact between the TFT panel and the glass supportplate increases. After the TFT panel is flat against the glass supportplate, the resin is cured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b illustrate a laminating chuck in accordance with apreferred embodiment.

FIG. 2 is a plan view of the laminating chuck shown in FIG. 1 detailingthe chuck's gas connections and instrumentation.

FIGS. 3 a and 3 b illustrate a sealing cover in accordance with apreferred embodiment.

FIGS. 4 a and 4 b illustrate another view of the sealing cover shown inFIG. 4.

FIG. 5 illustrates a TFT panel being laminated in accordance with apreferred embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 a and 1 b illustrate a lamination chuck 10 machined out of acast aluminum plate to maintain its flatness and dimensional stability.The top surface of the chuck 10 is machined into a 3 mm deep tray orpressure chamber cavity 11, which is slightly larger in length and widththan the active area of a TFT panel, thereby forming a ridge 12 on asecond edge 17 of the chuck 10, third edge 18 of the chuck 10, andfourth edge 19 of the chuck 10, leaving the first edge 16 of the chuck10 without a ridge. No ridge is formed on the first edge 16 of the chuck10 because the TFT panel 100 (see FIG. 5) preferably has active elementsextending all the way to the first edge of the panel (the chest walledge). Sealing tape (not shown) is affixed to the ridge 12 to helpmaintain desired pressure. The side walls 13 of the chuck 10 arerecessed to form a shoulder 14 on all four sides, onto which an adhesivetape drip skirt (not shown) is attached. The drip skirt is used to helpcatch excess UV-curable resin that escapes from the sides of the chuck10 during lamination. Vacuum channels 15 are machined into all threesides of the ridge 12 so that the TFT panel can be held firmly in placeby three of its edges.

FIG. 2 illustrates the lamination chuck 10 in plan view. An input port20 leads to a recess 11 that serves as a pressure chamber during thelamination process. N₂ gas enters the input port 20 through a pressurehose 26 and pressure regulator 26 a. Two bleed holes 21 allow excess gasto escape through a needle bleed valve 22, and two pressure sensingholes 23 allow the pressure inside the pressure chamber 11 to bemonitored by a manometer 24. A second pressure hose 27 connects themanometer 24 to the pressure sensing holes 23. Suction is applied to thevacuum channels 15 by a vacuum connection hose 25 leading to a vacuumpump (not shown), which may be of the type used for vacuum chucks usinglint-free paper.

Preferably, the holes 21, 23 are positioned as close to the ridge 12 aspractical to avoid uneven reflection of UV radiation that is used forcuring the UV-curable resin. Preferably, the pressure chamber 11 issandblasted and the entire chuck 10 is anodized black to minimizereflection of the UV radiation that may cause exposure intensityvariations. Preferably, all four sides of the chuck 10 are covered witha Teflon tape 101 (FIG. 6) to avoid scratching the TFT panel, and inparticular, bonding pads and pad routing lines on the TFT panel'speripheral strips.

FIGS. 3 a and 3 b illustrate a vacuum sealing cover 40 that is used toprevent the TFT panel 100 from sagging while on the chuck 10. Twohandles 41 are mounted on the top side of the sealing cover 40. Asealing cover vacuum channel 42 is formed at the underside of thesealing cover 40. This sealing cover vacuum channel 42 is connected to avacuum port 43 positioned at the top side of the sealing cover 40, andthe vacuum port 43 is connected to a vacuum pump (not shown). Suctionmay then be applied through the sealing cover vacuum channel 42 to allowthe sealing cover 40 to hold the TFT panel 100 straight and prevent itfrom sagging down. A bleeder valve port 44 located on the underside ofthe sealing cover 40 is connected to a bleeder valve knob 45 on the topside of the sealing cover 40 to regulate suction within the sealingcover vacuum channel 42. Sealing tape 46 is affixed around the vacuumchannel 42 and around the edges of the underside of the sealing cover 40to help maintain the desired suction. FIGS. 4 a and 4 b also illustratethe sealing cover 42 of FIG. 3.

The chuck 10, the glass support plate and a UV-curable resin arepreheated to 50° C. to reduce the viscosity of the resin. The chuck 10is preferably heated with a resistance element (chuck heater)(not shown)and a thermocouple (not shown) is used to monitor the temperature of thechuck 10. The glass support plate and the resin are preferably heated ina convection oven.

As illustrated in FIG. 5, the TFT panel 100 is positioned on the chuck10 with the back face (the face to be laminated) up and the front face(the face carrying the TFTs) down. Locating pins (not shown) are used toprecisely align the TFT panel 100 on the chuck 10. The vacuum hoses 25(FIG. 2) are connected and the vacuum pump is turned on. The drip skirt(not shown) is applied to the second edge 17, third edge 18, and fourthedge 19 of the chuck 10 (FIG. 1). The sealing cover 40 is placed on topof the TFT panel 100 with the vacuum channel 42 near the chest wall edgeof the TFT panel 100. Vacuum is applied to the channel 42 to straightenthe TFT panel 100 so the drip skirt can be applied to the panel whilethe panel is straight. The pressure is regulated, preferably to apressure of 1.2 inch water column (WC). The bleed valve 22 is partlyopened to stabilize the pressure and to allow for pressure reductionlater. At a pressure of 1.2 inch WC the TFT panel 100 bows up and out toform a dome that is approximately 1 mm high in the center. The resin ispoured onto the glass support plate 102 or on the bottom face of the TFTpanel 100, preferably in a dog-bone shape or an oval shape puddle, withthe long axis of the puddle parallel to the longer dimension of theglass support plate 102. The glass support plate 102 is then guided bylocating pins (not shown) onto the TFT panel 100 where it is let standfor a length of time, preferably five minutes. In this position,initially only the center of the TFT panel 100 makes contact with theglass support plate 102 causing the excess resin to be squeezed awayfrom the center. Over another length of time, also preferably fiveminutes, the pressure in the pressure chamber 11 is reduced linearlyfrom 1.2 inch WC to 0.3 inch WC. As the pressure is reduced, the domeflattens out and the excess resin is squeezed out into the drip skirt(not shown). At 0.3 inch WC, the TFT panel 100 is planar. This techniquehelps to minimize the occurrence of air-bubbles in the resin. Over asettling time, preferably five minutes, potential variations in resinthickness will smooth out. The resin is UV cured with light from a UVsource (not shown), preferably for 240 seconds, a shorter length of timethan that which is required for the previous method of manufacture.

1. A method of laminating a relatively thick glass support plate to arelatively thin, rectangular TFT panel, said panel having a front facecarrying thin film transistors (TFTs) associated with respective pixelpositions over an area that stops short of extending to the edge of thepanel on at least 3 edges leaving at least 3 respective peripheralstrips of the front face of the panel that are free of TFTs, comprising:supporting the TFT panel over a cavity in a lamination chuck makingphysical contact with said peripheral strips of the panel and holdingsaid peripheral strips to the chuck by vacuum suction, positioning thefront face of the panel to face the cavity and having a back face of thepanel facing away from the cavity; applying fluid pressure to thecavity, supporting a central portion of the TFT panel so the TFT paneldoes not bow in toward the cavity; uniformly applying a UV-curable resinbetween a front face of the glass support plate and the back face of theTFT panel; gradually moving the glass support plate and the TFT paneltoward each other until the back face of the panel is laminated to thefront face of the plate, with said UV-curable resin between the paneland plate; and curing the resin with UV light to complete thelamination.
 2. The method of laminating a relatively thick glass supportplate to a relatively thin, rectangular TFT panel as in claim 1, whereinsaid applied fluid pressure is gas pressure.
 3. The method of laminatinga relatively thick glass support plate to a relatively thin, rectangularTFT panel as in claim 1, wherein said UV curable resin between the paneland the plate has a uniform thickness and is free of bubbles.
 4. Amethod of laminating a relatively thick glass support plate to arelatively thin, rectangular TFT panel, said panel having a front facecarrying thin film transistors (TFTs) associated with respective pixelpositions over an area that stops short of extending to the edge of thepanel on at least 3 edges to thereby leave at least 3 respectiveperipheral strips of the front face of the panel that are free of TFTs,comprising: supporting the TFT panel over a cavity in a lamination chuckthat makes physical contact with said peripheral strips of the panel andholds said peripheral strips to the chuck by vacuum suction, with thefront face of the panel facing the cavity and a back face of the panelfacing away from the cavity; applying fluid pressure to the cavity toforce a central portion of the TFT panel to bow out, away from thecavity; applying UV-curable resin to at least a central portion of atleast one of the glass support plate and the TFT panel; gradually movingthe glass support plate and the TFT panel towards each other toinitially cause only central areas thereof, at least one of which hassaid resin thereon, to make contact with the resin and each other andthereafter to gradually spread the resin between the plate and the panelwhile increasing the area over which resin covered surfaces of the plateand panel make contact, and gradually reducing the gas pressure in thecavity, until the entire back face of the panel is laminated to theplate, with a layer of resin between the panel and plate; and curing theresin with UV light to complete the lamination.
 5. The method oflaminating a relatively thick glass support plate to a relatively thin,rectangular TFT panel as in claim 1, wherein said applied fluid pressureis gas pressure.